The present invention relates to a direct current motor.
Japanese Laid-Open Utility Model Publication No. 53-73403 discloses a direct current motor including a rotor provided with a core, a plurality of commutator segments, and a coil. The core has a plurality of teeth arranged along a circumferential direction, with each tooth extending along a radial direction of the rotor. The plurality of commutator segments are arranged inward from the plurality of teeth in the radial direction of the rotor along the circumferential direction of the rotor. Each of the commutator segments has a planar surface extending along the radial direction of the rotor (direction orthogonal to rotor axis). The coil is formed by continuously winding a conductive wire around the plurality of teeth. The motor further includes a stator and a brush. The stator has magnets facing the outer surface of the teeth in the radial direction of the rotor. The brush is held by a brush holder, which is fixed to the stator, and is pressed in an axial direction of the rotor to come in contact with the commutator segments. Such a motor enables more miniaturization in the axial direction than, for example, a motor in which commutator segments are arranged cylindrically at positions shifted from the coil in the axial direction and a brush is pressed from the outer side in the radial direction of the rotor to come in contact with the commutator segments.
However, the rotor described in Japanese Laid-Open Utility Model Publication No. 53-73403 is enlarged in the radial direction of the rotor since the teeth (coil) and the commutator segments are arranged next to one another in the radial direction of the rotor. In other words, the outer diameter of the rotor, and ultimately, the outer diameter of the motor, increases when enlarging the contact range (contact area) in the radial direction between the commutator segments and the brush. If the outer diameter of the motor is limited, the contact range (contact area) in the radial direction between the commutator segments and the brush would decrease such that a large amount of current cannot be supplied from the brush to the coil via the commutator segments. As a result, the generation of a high output with the motor becomes difficult.